My 1.5yo wandering garter is only just now at 12". I feed him 7-10 rosies per week. Out of that he will generally eat 3-5 immediately after I put them in his cage and then save the rest for the following day or two. Out of that bunch he usually will either attack and kill 2-3 and leave them for me to discard or ignore them entirely. I would say on average he eats about 5-7 rosies per week when all is said and done.